The present invention relates to processes for purifying methylsilane. More particularly, the present invention provides for purifying and condensing methylsilane gas through cryogenic adsorption techniques.
Organosilicon gases, particularly methylsilane are employed in the semiconductor industry as coatings and films. A typical process for producing methylsilanes is called the xe2x80x9cdirect process.xe2x80x9d This is the reaction of methyl chloride and silicon in the presence of a copper catalyst. The effluent from the reactor, however, is still a mixture of methylsilanes and high boiling materials such as disilanes, polysiloxanes, silylmethylenes and the like. This effluent must then be distilled to separate the methylsilane from the other silanes present.
Additionally, these synthesis methods also result in the generation of olefinic and chlorinated hydrocarbons. These individual species can cause separation problems with the above-mentioned distillation process, as well as problems relating to color and stability of the resulting product.
A typical sample of methylsilane gas may find various impurities in it that can interfere with the use of methylsilane in semiconductor fabrication and processing. These impurities include for example hydrogen, nitrogen, argon, oxygen, methane, ethane, carbon dioxide, silane, chlorosilane and dimethylsilane.
Applicants have discovered that the use of a cryo-adsorption process will remove impurities, particularly chlorosilanes and carbon dioxide, better than processes such as distillation.
The present invention provides for a process for the purification of methylsilane. The process provides for the steps of providing a source of methylsilane containing impurities, directing the methylsilane to an adsorption vessel for adsorption and degassing and directing the purified methylsilane to a collection vessel.
The adsorption vessel will contain an appropriate adsorbent such as magnesium silicate and will be kept at a temperature of about xe2x88x9240xc2x0 C.
The impurities typically found in methylsilane gas are hydrogen, nitrogen, argon, oxygen, methane, ethane, carbon dioxide, silane, chlorosilane and dimethylsilane.